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Abstract

The need for miniaturized, portable devices to separate and detect unknown compounds has greatly multiplied, leading to an increased interest in microfluidics. Total integration of the detector and pump are necessary to decrease the overall size of the microfluidic device. Using previously developed thin film technologies, an electroosmotic flow (EOF) pump was incorporated in a microfluidic liquid chromatography device. An EOF pump was chosen because of its simple design and small size. EOF pumps fabricated on silicon and glass substrates were evaluated. The experimental flow rates were 0.19-2.30 microliters/minute for 40-400 V. The theoretical pump efficiency was calculated along with the generated mechanical power by various pump shapes to elucidate more efficient pump designs. To better understand the EOF on plasma enhanced chemical vapor deposition (PECVD) silicon dioxide, the zeta potential was investigated. PECVD oxide is amorphous and less dense than thermal silicon dioxide, which slightly changes the zeta potential. Zeta potentials were found for pH values from 2.6 to 8.3. Also, surface defects that affect the zeta potential were observed, and procedures to detect and prevent such defects were proposed. Finally, surface modifications to the microfluidic device were attempted to demonstrate that thin film EOF pumps can be used in the liquid chromatographic separation of mixtures. The microfluidic separation channel was coated with chlorodimethyloctadecylsilane, however, due to problems with channel filling and reservoir adhesives, separation was not achieved. The use of new adhesives and external pumps were proposed to resolve these problems for future testing. Also new methods to combine EOF pumps with microfluidic channels and on-chip detectors were suggested.